The proposed study investigates word retrieval processes involved in speech production and recognition. In particular, the role of the 'phonological neighborhood' is assessed in non-brain-damaged (NBD) subjects and in subjects with aphasia. As words are being retrieved for production, related words also become available, and are sometimes produced instead of the intended word, resulting in phonologically related (similar- sounding) speech errors. In language comprehension, words which sound similar to the target may interfere with the recognition of the word produced. These observations prompted researchers to assess whether the number of words similar to a target (its 'neighborhood density') influences the speed and accuracy of its retrieval. Studies with normal speakers show that the more neighbors a word has, the harder it is to recognize, but the easier it is to produce. Research with older subjects has suggested that increased word recognition problems in aging may be due to difficulties inhibiting incorrect words from the set of activated alternatives, while increased word production problems may be due to reduced transmission of activity throughout the lexicon. Similar problems have been hypothesized for aphasic populations. Examining the influence of a word's neighborhood density is 1 way to illustrate such effects; however, no effort has been made to reconcile the disparate findings in recognition and production within the same theoretical framework. The current study addresses this gap, by extending the study of phonological neighborhood effects, in both recognition and production, to older NBD and aphasic speakers. 2 main studies are proposed: Study 1 tests for competitive neighborhood effects in the word recognition of NBD (young and old) and aphasic subjects, using word recognition tasks. Study 2 tests for facilitative neighborhood effects in speech production, using naming tasks with the same groups. The proposed study aims to clarify the processes of word recognition and word production in non-brain- damaged speakers, and examine the ways in which these processes can break down with brain damage. Knowledge of the effects of aging is essential to an understanding of language impairments that occur in aging populations, such as aphasia and dementia. It is only through such an understanding that effective methods can be developed to treat word retrieval deficits that arise from brain damage. [unreadable] [unreadable] [unreadable]